The process of catalytic oxidation of hydrogen chloride with oxygen in an exothermic equilibrium reaction developed by Deacon in 1868 was the beginning of industrial chlorine chemistry. However, chlor-alkali electrolysis pushed the Deacon process far into the background. Almost all chlorine production has taken place by electrolysis of aqueous solutions of sodium chloride. In recent times, however, the Deacon process is becoming more attractive again as worldwide chlorine requirements are growing more strongly than demand for sodium hydroxide, a co-product of electrolysis. This development is accommodated by the process for the production of chlorine by the oxidation of hydrogen chloride, which is uncoupled from the production of sodium hydroxide. Moreover, the starting product hydrogen chloride is readily accessible; it is obtained in large quantities as a co-product, for example in phosgenation reactions such as isocyanate production.